A wide range of invasive and exploratory medical procedures are performed with the aid of fluoroscopic imaging equipment for monitoring progress. Fluoroscopy provides “real-time” radiographic imaging that may be particularly useful for tracking motion that is related to a diagnostic procedure and is often used to monitor progress of an iodinated contrast agent or to help a practitioner in guiding a catheter through the veins of a patient in order to reach a location in the patient's body that requires some form of treatment, e.g., the site of a tumor or abscess.
The fluoroscopy-guided process of catheter placement and guidance requires considerable skill and often entails an amount of risk. Guidance procedures may be time consuming and may be difficult to execute, since the ability to visualize a catheter tip as it progressively advances through complex venous structures is inhibited by problems such as poor subject contrast, obstructed visibility, and dose constraints. Once a catheter is appropriately positioned, a treatment delivery device may be inserted through the catheter to the site of the abnormality and a treatment applied. For example, the treatment may involve embolization to cut off the blood supply that feeds a tumor, or to ablate a tumor using thermal methods, or, in the case of an abscess, to drain infectious material.
Conventionally, radiographic imaging to support state-of-the-art interventional procedures uses expensive, specialized C-arm systems that position the x-ray source and detector in fixed position with respect to each other and allow a limited level of flexibility in placement of the source-detector pair about the object that is to be imaged. C-arm fluoroscopy systems are equipped with high frame rate flat panel detectors that provide two-dimensional (2-D) images. Supporting components for these imaging systems may include heads-up monitors, for example, that allow the practitioner to view the progress of an interventional procedure, such as catheter insertion or a surgical operation.
One limitation of conventional imaging systems used for fluoroscopy relates to the need for repositioning of C-arm components at various points during a procedure. Visibility of a catheter device or of contrast agent progress may be obscured at particular angles or positions so that adjustment of source and detector positioning is required in order to maintain useful tracking. In some cases, the needed movement of the C arm may interfere with the procedure or require that the practitioner shift position to allow C arm movement, which can be undesirable.
Another limitation of conventional imaging systems used for fluoroscopy relates to the lack of depth information. Systems dedicated solely to fluoroscopic imaging are optimized to show movement in real-time, but provide only 2-dimensional (2-D) images to the viewer. A separate tomography or other depth imaging apparatus must be used if depth information is to be obtained.
Tomography (also referred to as x-ray computed tomography or computed tomography (CT)) is a well known medical imaging method that uses computer processing to acquire and combine image data from multiple angles. In computed tomography, digital image processing is used to generate a three-dimensional image of the inside of an object from a series/collection of two-dimensional x-ray images taken around a single axis of rotation. In an idealized CT apparatus, a source/detector makes one or more complete 360-degree rotations about the subject obtaining a complete volume of data from which images may be reconstructed. The volume of data produced by the CT system is manipulated to generate depth images of various internal structures. The images may be generated in the axial or transverse plane (e.g., perpendicular to the long axis of the body), or reformatted in various planes, or volumetric three-dimensional representations.
Tomosynthesis combines digital image capture and processing with some portion of the source/detector motion used in tomography. While there are some similarities to CT, tomosynthesis has a number of differences from CT as conventionally practiced and is largely considered as a separate technique. As noted above, in CT, the source/detector makes a complete 360-degree rotation about the subject obtaining a complete set of data from which images may be reconstructed. By contrast, digital tomosynthesis uses a small rotation angle (e.g., 30 degrees) with a small number of discrete slices/exposures (e.g., 25-70 exposures). This set of data, incomplete with regard to full volume image information, is digitally processed to yield images similar to tomography but with a broader depth of field. Since the image is digitally generated and represented, various processing techniques may be used to generate and present a series of slices at different tissue depths and with different thicknesses reconstructed from the same image acquisition, thereby saving time and reducing radiation exposure.
Acquired tomosynthesis data may be incomplete in terms of the full three dimensions of data content. Tomosynthesis offers higher depth resolution in image slices parallel to a detector than CT offers, while CT may provide better isotropic resolution. Tomosynthesis is advantaged over 2-D radiography as it provides a measure of depth detail that is not otherwise available with conventional radiography. Moreover, the limited depth detail information that it offers can be of value to supplement fluoroscopic display. The resulting depth display provides improved visualization over conventional 2-D image presentation and, even though it may not be available in real-time as is 2-D fluoroscopy, tomosynthesis imaging, if performed at near real-time speeds, could be particularly helpful for guiding interventional procedures.
Thus, it can be seen that there is a need for a portable imaging apparatus that is capable of providing fluoroscopic imaging as well as depth imaging such as tomosynthesis imaging to help track progress for clinical and interventional procedures. There would be particular value in imaging apparatus and techniques that allow an imaging apparatus to switch rapidly between depth imaging and fluoroscopy at suitable angles, without requiring corresponding repositioning of the x-ray sources and detector.